WEST POINT, N.Y.—The military needs to rethink how it teaches character and ethics, eschew staid briefing slides and avoid disciplining subordinates via email, the nation's top uniformed officer said Thursday.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, visited the U.S. Naval Academy and the U.S. Military Academy this week, as part of a series of talks emphasizing the need to focus on ethics. In meetings with students,...